Integrated circuit manufacture is a multi-step construction process. The process entails repetitive steps of lithography to selectively expose underlying layers, etching of partially or completely exposed layers, and deposition of layers or filling of gaps frequently produced by etching or selective deposition of materials. Etching of metals is a critical process step. Frequently metals must be selectively etched in the presence of other metals, metal alloys, and/or non metal materials without corroding, etching, or oxidizing the adjacent materials. As the dimensions of the features in the integrated circuit become increasingly smaller, the importance of minimizing corrosion, etching, oxidizing, or other damage to adjacent materials and features increases.
The structural features and compositions of the other metals, metal alloys, and non metal materials may vary depending on the particular device so that prior art compositions may not etch the specific metal without damaging the materials in adjacent structures. Combinations of particular adjacent materials may also affect the type and amount of damage produced in an etching step. Thus, it is often not obvious which etch composition is appropriate for a given device structure and adjacent materials.
A particular problem is the etching of NiPt over a NiPt silicide layer in the presence of other metals. The use of aqua regia based etching or other known NiPt chemistry successfully etches the NiPt but typically damages or oxidizes other metals. When using aqua regia based chemistry, the etch selectivity of the NiPt relative to the NiPt silicide is unsatisfactory and typically results in a silicide surface deficient in nickel and platinum species (e.g. Pt or PtOx) and also an unsatisfactorily high level of silicon oxides deep into the film. PtOx species appear to etch slower in aqua regia type etchants. Compositions employed in a process providing a surface enriched in PtOx species may help protect the underlying NiPt silicide from excessive oxidation and etching.
It is an objective of this disclosure to provide compositions and processes which are suitable to etch NiPt in the presence of NiPt silicides with greater selectivity, with decreased silicon oxidation and, without significant damage to other metals typically employed in semiconductor fabrication.